Japanese Patent Laid-Open Publication No. 2003-298919 describes a digital camera having such synthesis means. The digital camera described in the publication comprises an image-capturing system having a telescopic lens and an image-capturing system having a wide-angle lens. A single subject can be captured essentially simultaneously at different angles of view by means of both image-capturing systems. This digital camera synthesizes a wide-angle view and a telescopic view, both of which have been obtained through image-capturing operation, and stores the thus-synthesized image.
Although the digital camera described in the patent publication stores a synthesized image, large-capacity storage means is required, because the synthesized image is large in file size. When a wide-angle view and a telescopic view are synthesized together, the number of pixels of the wide-angle view is usually increased by means of interpolation so as to match the number of pixels of the telescopic image, and the wide-angle image complemented with the pixels and the telescopic image are synthesized together. As a result, the file size of the synthesized image data is significantly increased.
For instance, each of a pre-interpolation wide-angle image and a telescopic image is assumed to have 2592 (width)×1944 (length) pixels (about 5 million pixels). A wide-angle lens used for capturing a wide-angle image has a 35 mm-film equivalent focal length of 48 mm, and the telescopic lens used for capturing a telescopic image has a 35 mm-film equivalent focal length of 96 mm. In this case, the range of a field expressed by one pixel in a wide-angle image is expressed by four pixels in the telescopic image. For instance, when an image of an object of predetermined size has been captured, the object is expressed by “n” pixels in a wide-angle of image and expressed by n×4 pixels in a telescopic image. In other words, a scale of 1:2 exists between a wide-angle image and a telescopic image.
In order to synthesize the telescopic image and the wide-angle image together without involvement of a decrease in the number of pixels of the telescopic image, the wide-angle image must have been previously enlarged double in both the vertical and horizontal directions by means of interpolating pixels. More specifically, the wide-angle view must have been enlarged to an image of 5184×3888 pixels. The number of pixels of a synthesized image, which is obtained by synthesizing the wide-angle image having undergone pixel interpolation with the telescopic image, comes to as many as about 20 million.
An increase in file size resulting from synthesis of the images becomes more noticeable with increasing ratio of the focal length of the wide-angle image to the focal length of the telescopic image. When the focal length ratio is assumed to be “n,” the number of pixels of the synthesized image is simply calculated as n2 times the number of pixels of a pre-synthesis image. The synthesized image of such large volume puts a significant squeeze on the finite storage capacity of the digital camera.